Hot cathode electron discharge tube



H. M. FREEMAN ET AL HOT CATHODE ELECTRON DISCHARGE TUBE Original FiledJan.

May 7, 1935.

ESSES n s www v ATTO'RNEY Patented May 7, 1935 UNITED STATES HOT CATHODEELECTBON DISCHARGE TUBE Hubert M. Freeman. deceased, late of EastPitteburgh, Pa., by Max F. neges, administrator, Bloomfield, N. J., andWallace G. Wade, Philadelphia, Pa., assignors to Westinghouse Electricand Manufacturing Company, a corporation o! Pennsylvania Originalapplication January 8, 1923. Serial No. 611,263. Divided and thisapplication Jnnezl, 1932, Serial No. 619,600

9 Claims.

The invention relates to hot-cathode electron discharge tubes and it hasparticular relation to grid-controlled discharge tubes in which theelectron-emitting cathode is so heated from a source of alternating; orfluctuating, current as to substantially eliminate the undesirableeffects of the varying heating current upon the electron flow in thetube.

Several cathode structures embodying the foregoing features have beendisclosed in our copending application, Serial No. 611,263, filedJanuary 8, 1923, of which the present application is a division. Thisapplication is also a substitute for a divisional application Serial No.120,580, led July 6, 1926.

.Among the objects of the invention is the provision of a cathodeelement comprising an electron-emitting cathode surface element and anelectrically distinct heating element so associated therewith that thefluctuations of the current in the heating element, whenv energized froman alternating-current source or the like, do not interfere, orotherwise exert a controlling action, upon the ilow of electrons fromthe cathode element to the other space-current electrodes of the tube. v

According to the invention, a heater element which may be in the form ofa U-shape wire, or the like, with its two legs placed close together, soas to render it substantially non-inductive, is encased in a tubularheat-conducting sheath, the surface of which is adapted to emitelectrons when heated. In order to secure prompt electron emission uponturning on the heating current for the cathode, the body of the cathodestructure is made relatively small, eliminating excess material that isto be heated. To this end,l the cathode sheath is secured directly uponthe U shape heating wires and is insulated therefrom by an oxide coatingwhich is provided either on the surface of the electron-emitting sheathor on the heating wire disposed therein, or on both.

Our invention will be best understood from the accompanying drawing, inwhich Fig. 1 is a view, partially in elevation and par? tially insection, of a thermionic tube, with the associated circuits shown indiagrammatic form, embodying the invention, and Fig. 2 is an enlargedhorizontal sectional view along the line II--II of the cathode of Fig.1.

Referring to the drawing, which illustrates the invention as applied/toa radio-receiving tube of a familiar type, an elongated envelope i ofglass or the like, has a re-entrant stem 3 termi- '3 mating in a press 4into which are welded ve (ci. 25o-21.5),

lead-in wires l to Il, which serve to support, and to provideconnections to, a cathode member II, a grid I2 and a plate Il arrangedconcentrically In the usual way.

'I'he cathode member II, to which this invention particularly relates,comprises a pair of parallel-disposed wires I5 bent to form asubstantially U-shape heater element supported at its two ends by theends oi.' the two lead-in wires 1 and 8, which serve to supply theretothe heating current. The bent portion connecting the two wires I5 issupported at the top of the tube by means of a carrier rod II extendingfrom leadin wire 6, the latter serving also to make connection to theelectron emitting surface of the cathode element, as will be describedhereinafter. 'I'he electron-emitting cathode element of the tube isconstituted by an oxide coated platinum wrapping 2l surrounding the twoheating wires I5. The Wrapping is formed by helically winding anoxide-coated strip of platinum, or other suitable material, around thetwo sections of the heater element I5. The turns of the helix thusconstitute an equi-potential sheath or tube en- In the form of theinvention shown in Figs. 1 Y

and 2, the insulation is provided by the oxide coating 22 on the stripconstituting the wrapping 2|, thus securing a very good heat exchangebetween the wires of the heating element and the body which is to beheated to the temperature of electron emission. If additional insulationis necessary, the wires l5 of the heating element itself may be coveredby a layer 23 of some insulating material, for instance in the form ofan oxide, such as magnesium oxide. which may be made to adhere to thesurface of the heating wire in a way similar to the oxides on theplatinum strip, of which the wrapping 2i is made.

As stated before, the connection to the electronemitting surface elementof the cathode is made independently of the connection to the heatingcarrier rod I1.

wires il, for instance, by means of a strip 24 extending from theplatinum wrapping 2| to the which is connected to the terminals of theheating wires I5, thus eliminating the diiiiculties incident to theheating-current supply of prior art tubes. v

The cathode, grid and anode terminal wires t, 9 and I0 may be connectedin the usual way. When operating as an ampliner, for instance, theconnections may comprise input leads 26 connected to the grid andcathode element, while the output circuit may comprise a detecting orload device 21 connected in series with a source of plate voltage 2lbetween the cathode lead-in wire Il and the cathode lead-'in wire I. Y

The novel features of the invention, which are based on the idea ofsecuring a compact and efcient cathode structure for alternating-currentheated tubes by adheringlv uniting the insulating spacing memberinterposed between the outer cathode sheath and the heating wiresembodied therein with the surfaces of the sheath or heating wire may beembodied in a variety of other structures which will readily suggestthemselves to those skilled in the art.

We claim as our invention:

1. A thermionic cathodeA electron-discharge tube comprising a cathodestructure comprising a U-shape heating wire having closely disposedparallel heater sections and a tubular sheath comprising platinum stripwound about said heater sections, the outer surface of said sheath beingadapted to emit electrons when heated, and a surface layer of insulatingoxide intervening between said heater sections and said sheath.

2. A thermionic cathode electron-discharge tube comprising a cathodemember comprising a U-sha'pe heating wire'havingclosely disposedparallel heater sections and a tubular sheath of` tions, the outersurface of said sheath being -adapted to emit electrons when heated,said sheath comprising a helically wound strip of conducting materialhaving an oxide coated surface engaging the surface of said heatersections.

' 4. An electron-discharge tube, comprising a cathode structurecomprising an electrically conducting heating element, an electricallyconducting strip having an electron-emitting surface of strontium oxidewound about said heating element and electrically insulated therefrom bymeans of magnesium oxide.

5. An equipotential cathode structure comprising an equipotentialsurface, a substantially non-inductive electrical heater for renderingsaid surface thermionically active, said non-inductive heater having aninsulating layer adhering to its outer surface.

6. An equipotential cathode structure comprising an equipotentialsurface, a two leg heating wire having closely disposed heater sectionswithin said equipotential surfaceand an insulating heat-resistingcoating formed on said heater sections and adhesively bound thereto.

7. An electron discharge device comprising a plurality of cooperatingelectrodes, at least one of said electrodes being an indirectly heatedelectron-emitting cathode comprising a metallic sleeve serving as anelectron-emitter and a heater surrounded substantially by said sleeve,but maintained out of direct electrical contact therewith, said heatercomprising a two-leg electric conductor anchored about its center andconnected l at its ends to lead-in conductors and comprising rectlyheated cathode comprising a metallic cath-r ode sleeve serving as anelectron-emitter, a filamentary heating element having a plurality oflegs for heating said cathode sleeve and adjacent thereto, and aninsulating, refractory coating, containing an insulating compound of anelement having' a low atomic number, on said heating element and beingnormally substantially non-conductive and solid at the operatingtemperatures of said heating element and adhesively bowed to at least apart of said heating element.

, MAX F. REGES. Administrator of the Estate of Hubert M. Freeman,Deceased.

WALLACE G. WADE.

Cyl

